La 3419751995

International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
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Gyadari Ramesh, Dr.G.Chandra Mohan Reddy / International Journal Of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 4, Jul-Aug 2013, pp.1975-1995 1975 | P a g e Analysis of Optimization of Blank Holding Force In Deep Drawing By Using LS DYNA Gyadari Ramesh, Dr.G.Chandra Mohan Reddy Department of Mechanical Engineering, Osmania University, Hyderabad-500085. ABSTRACT Sheet metal forming problems are typical in nature since they involve geometry, boundary and material non-linearity. Cup drawings involves many parameters like punch and die radius, clearance, lubrication, blank holding force and its trajectories etc. So designing the tools for cup drawing involves a lot of trial and error procedure. To reduce number of costly trial error steps, the process can be simulated by using finite element packages. Even the finite element package gives an approximation towards the solution. The experimentation is inevitable. The aim is to study analysis of optimization of blank holding force developed for cup drawing operation by using explicit finite element package LS DYNA. One of the basic problems in deep drawing is wrinkling. Wrinkling can be avoided by using blank holding force. But higher the blank holding force (BHF), higher is the frictional force, so more will be tensile stresses in cup wall there by promote tearing failure at the punch corner. Hence BHF needs to optimized so as to prevent the wrinkling and at the same time to prevent tearing failure. In this work die design is done for a cup of 30mm diameter and deep with 1 mm thickness. For the same blank holding force is calculated from the empirical formula. The same is simulated on an explicit finite element package LS DYNA. By an iterative procedure the optimum blank holding force is obtained and presented. B H F in deep drawing is an essential parameter to be determined optimally to avoid formation of wrinkles. It is also necessary to at the same time to determine the force in drawing operation and failure of the cup. Higher the B H F, higher is the frictional forces between the blank and blank holder, so higher the loads required for drawing operation and higher the strains developed in the cup walls between the die and punch, thereby reducing thickness of the section. In this thesis optimum blank holding force has been found out by checking the condition of nonformation of wrinkles at different coefficient of friction at (0.045, 0.06, 0.1, 0.13, and 0.15) and at different die radius (2, 3, 4, 5,6mm) and the values of blank holding force has been taken where no wrinkles has been formed for different coefficient of friction and for different die radius and the graphs are plotted and the results are studied. h- Method is used for mesh convergence stability of max vonmises stress is taken as a parameter to check the convergence. Keywords – Deep Drawing by Using LS DYNA, Blank Holding and blank holding force (BHF). I. INTRODUCTION Sheet metal forming is one of the most widely used manufacturing processes for the fabrication of a wide range of products in many industries. The reason behind sheet metal forming gaining a lot of attention in modern technology is due to the ease with which metal may be formed into useful shapes by plastic deformation processes in which the volume and mass of the metal are conserved and metal is displaced from one location to another. Deep drawing is one of the extensively used sheet metal forming processes in the industries to have mass production of cup shaped components in a very short time. In deep drawing, a flat blank of sheet metal is shaped by the action of a punch forcing the metal into a die cavity Sheet metal forming is one of the most common manufacturing processes to plastically deform a material into a desired shape. Products include hundreds of automotive components, beverage cans, consumer appliances, submarine hulls, and air craft frames. Based on the geometry, the volume and the material, sheet metal forming can be divided into various categories such as stamping, deep drawing, stretch forming, rubber forming, and super plastic forming. Among these, Stamping and deep drawing are the most common operations. Deep drawing products in modern industries usually have a complicated shape, so these have to undergo several successive operations to obtain a final desired shape. Trimming of the flange is one of those operations and that is used to remove the ears i.e. to have uniform shape of the flange on all the sides of the final product. These are formed due to uneven metal flow in different directions, which is primarily due to the presence of the planar anisotropy in the sheet. The main concern of the deep drawing industry is to optimize the process parameters in order to get a complete deep drawn product with least effects and high limiting drawing ratio. In order to achieve this optimization objective a large number of solution runs need to be performed in order to search for the optimum solution. Furthermore, the quality of Gyadari Ramesh, Dr.G.Chandra Mohan Reddy / International Journal Of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 4, Jul-Aug 2013, pp.1975-1995 1976 | P a g e the products can be increased. With reference to an economical success it is very important to put better and cheaper products faster on the market than other competitor‟s. A substantial aid for this is the numerical simulation. Costs and time for tool adapting could play an outstanding roll. Furthermore, changes in design while fabricating a prototype are usual. By means of numerical simulation, potential forming problems can be recognized during fabricating a first tool. Despite many advantages of the numerical simulation, it must be said, that there are costs for hardware, software, training and for the simulation itself. However, it is an effective means for making forming processes and new products cheaper. Tool loads can be computed and overloads can be predicted by means of FEM, which is very difficult in practical experiments. The depth of draw may be hallow, moderate or deep. If the depth of the formed cup is more than its diameter, the process is called Deep Drawing. Parts of various geometric and sizes are made by drawing operation, two extreme example being bottle caps, automobiles panels etc. the simplest example is the drawing of a flat bottom cylindrical cup. In the drawing of a cylindrical cup, a round sheet metal blank, is placed over a circular die opening and is held in place with a blank holder. The punch travels downward and forces the blank into the die cavity, forming a cup. The important variables in deep drawing are the properties of sheet metal, the ratio of blank diameter to punch diameter, the clearance between the punch and die, the punch corner radius and die corner radius, the blank holder force, friction and lubrication. The forces occurring during drawing are bending at the radii, friction between blank holder and sheet metal, die and sheet metal, punch and sheet metal and compression at flange area or extremity of cup. Usually Drawing is a process of forming a flat, pre-cut, metal blank into a hollow shape, either cylindrical or box-shaped, by pressing it into a die cavity without excessive wrinkling, thinning, or fracturing. Typical parts produced by drawing include beverage cans, containers of all shapes and sizes, and automobile and aircraft panels. Deep drawing process is influenced by some parameters like residual stresses, Blank holding force etc. Residual stresses also play a very important role in how a formed part in a deep drawn cup. These stresses can become so large in a deep drawn cup that cracks are formed in the cup wall. These residual stresses can be removed by annealing the cup right after the deep drawing. However in most cases it is desire to avoid the annealing process. This process increases the production costs, and can lead to an inexpedient production flow and can give problems with regard to maintaining close tolerances due to distortion during annealing process. B H F is an important parameter in deep drawing process. It is used to suppress the formation of wrinkles that can appear n the flange of the drawn part. When increasing the B H F, stress normal to the thickness increases which restrains any formation of wrinkles. However, the large value of the B H F will cause fracture at the cup wall and punch profile. So, the B H F must be set to a value that avoids both process limits of wrinkling and fracture. Avoid wrinkling and tearing such that at ach punch travel (L), the following relations must be satisfied: FBH >F wrinkling and FBH